With the development of power electronics, various power electronics devices have been widely used in power system, industry, transportation, and household equipment. However, current harmonics and reactive power generated during application of power electronics devices can harm to the power grid. To overcome this problem, PFC circuits are generally applied in power electronics devices, such as in rectifiers or other switching power supplies, in order to keep the input current substantially in phase with the input voltage, thus lowering the harmonics and improving the power factor.